It is known that set "computer\administrative template\systems\logon\always wait for the network at computer startup and logon" to enable solves the slow logon problem most of the times. The question is what really slows down the computer startup. The userenv debug log did not give me much insights, so I began to reverse settings in the offending GPO appled to an ou containing the computer and, not long, found "computer\windows settings\security settings\file system" is the culprit. When I delete all the file system objects there, the startup of the computer is normal with the "....wait for the network..." set to disable. My guess is someone who really knows MS file system DACL and SACL can most likely provide some insight.
Any help is appreciated.